Please add support for CMake 3.16

[jhay06]

hi , i would like to ask if it is possible to support cmake 3.16 , i know that we can just upgrade cmake version but there are instances like on Ubports using clickable is still using 3,16 on its docker container for building app, i would like to add oatapp to UBports , but not possible since it requires version 3.20 and up thanks